Signal translating apparatus



March 18, 1947. RQSNEPVANGERS 2,417,712

'S1'.GrNAI.'r TRANSLATING APPARATUS Filed Nov. 1.8, 1944 IN VEN TOR.

RENE' s EPVANGERS Z BY @m- Patented Mar. 18, 1947 SIGNAL TRANSLATING APPARATUS Ren Snepvangers, .Haddon Heights, N. J., lassignor to Radio CorporationV of America, acorporation of lDelaware ApplicationNovember 18, 1944, Serial No.-`564,'145

9 Claims. l

This invention relates `to signal translating apparatus, and more particularly to a signal translating device of the capacity type adapted for use as a microphone or as a pick-up device in connection with phonograph records, the present invention being an improvement over that disclosed and claimed in the copending application of Chester M. Sinnett, Serial No. 414,305, led October 9, 1941, now Patent No. 2,376,456, granted May 22, 1945, and assigned to Radio Corporation of America.

In the aforesaid copending application, there is disclosed a capacity type pick-up whichV comprises ,asupporting member carrying a pair of electrodes in capacitative relation to each other, one of the electrodes being stationary andthe other being mounted on an expansible framework for vibratory movement relative to the stationary electrode. The movable electrode consists of a relatively thin, narrow, flexible strip of metal extending across the stationary electrode in spaced relation thereto,the exible strip being anchored.

at both its ends on the aforesaid framework. A needle is secured to the movable electrode substantially midway between its ends and is arranged to cooperate with the groove of a phonograph record. Movement of the movable electrode in response to the needle is confined substantially to a region in the vicinity of the needle to avoid vibration reflection from other parts of the movable electrode back toward the needle, thereby substantially eliminating distortion .fand extending the range over which the pick-up is operated with relatively great efficiency. A pick-up of this type is extremely light in weight, having a needle pressure of approximately grams. Such a pick-up may be connected in the tuning circuit of a suitable high frequency oscillator (for example, a 40 to 50 megacycle oscillator), and when the capacity of the `pickup is varied in response to the record, :it produces a frequency shift in the oscillator circuit and frequency modulation results. The frequency modulated signal may be passed through a suitable F-M channel rfor conversion into amplitude modulated signals and reproduction in known manner.

In the particular forms of pick-up disclosed in the aforesaid copending application of Sinnett, the stationary electrode and the flexible strip (in static condition) have opposed, facing, cooperative surfaces which lie in planes parallel to each other. The spacing between these electrodes is approximately 4 to 5 mils. It is apparent that, in approaching the stationary electrede in `response to signal forces applied-thereto through the'needle, the movable electrode must move through a distance less than the -air `gap between the electrodes to avoid making `contact with the .stationary electrode. Since, as pointed out above, the movement of the vibratory or movable electrode is confined to aregion substantially in the Vvicinity of the needle, it is further apparent that' only its central region will partake of useful movement, at best. Thus, `for a given movementfof the vibratory ribbon toward the stationary electrode, a relatively small change incapacity results, and `this limits lthe sensitivity of the device.

Another feature .of the Sinnett pick-up device is that the resonant frequency of vibration of the flexible, strip electrode thereof is controlled by expanding the expansible framework on which -it is mounted. `Since the vibratoryre'gion of the strip is under great tension, it becomes .set in its `stretched condition after a period `of use, and it then becomes necessary to slightly expand the `framework again. Upon continued expansion of the framework, the length of lthe -vibratory ribbon portion which cooperates with the stationary, plate electrode increases, and this has the effect of lowering the resonant .frequency .of the vibratory strip quite considerably.

The primary-object `of my present Vinvention is to provide an 'improved .signal translating device of the type set forth .above -Which `.will be free from the aforementioned diiliculties.

More particularly, it is an object of my present invention to provide an improved `capacity type signal translating device which .will have .much greater sensitivity than similar devices pro posed heretofore.

Another object-of my present invention Ais to provide an improved capacity type `pick-up as above ,set forth which will afford a .comparatively large gain insignal to noise ratio.

Still another object -of my present invention is to provide an improved capacity type pick-up Which is especially useful `in connection with phonograph records, -which will not-.cause the frecord with which it cooperates `during reproduction Ato radiate extraneous sounds, Vand which will Vnot itself'producesuchsounds AA further objectof my Vpresent invention `is to provide an improved capacity.typepick-.upwhich ywill loperate with a minimum of distortion.

Another object of my present ,invention is to provide an improved ,capacity .ty-pe` pick-up which is .very flexible in operation.

A .further .object of my present invention is to provide an improved capacity type pick-up of the character described in which the mass of the moving parts is very low.

Still a further object of my present invention is to provide an improved capacity type pick-up as above set forth which is extremely simple in construction, which can be easily manufactured Without requiring critical adjustments or extreme care during manufacture, and which is inexpensive in cost.

It is also an object of my present invention to provide an improved capacity type pick-up as above set forth which is sturdy in construction, the parts of which are easily accessible, which will have a long life, and which is highly eflicient 1n use.

In accordance with my present invention, I provide a yoke-shaped supporting member terminating in a pair of forwardly extending arms across the ends of which I mount a vibratory, conductive ribbon of resilient material in much the same way as in the pick-up device disclosed and claimed in my eopending application, Serial No. 538,834, iiled June 5, 1944, now Patent No. 2,397,888, granted April 2, 1946. Since the distance between. the yoke arms is constant, the length of ribbon between these arms always remains the same no matter what degree of tension is applied to the ribbon, and therefore its resonant frequency will remain constant. tween the yoke arms, I mount a block of insulating material for lineal adjustment relative to the active or vibratory portion of the ribbon electrode. A conductive plate electrode mounted on the insulating block is arranged to cooperate with the vibratory portion of the ribbon, the latter carrying a needle adapted to cooperate with phonograph records in the manner disclosed and claimed in the above identified copending application of Sinnett.

In its static condition, the vibratory portion of the ribbon has a plane surface facing the stationery, conductive electrode carried by the insulating block. The stationary electrode, on the other hand, is formed with a concave surface which faces the plane surface of the vibratory electrode or ribbon, the point of greatest or deepest concavity in the stationaryelectrode lying substantially opposite the point of attachment of the needle to the vibratory ribbon, It will be seen, therefore, that the spacing between the two electrodes is greatest behind this point of attachment, the curved or concave surface of the stationary electrode gradually approaching the ribbon in both directio-ns from the center thereof toward the ends. The curvature of the aforementioned concave surface of the stationary electrode may be a part of an ellipse or any other suitable surface of revolution.

Since the portions of the ribbon opposite the ends of the stationary electrode have practically no movement, the stationary electrode may be brought into sufficiently close proximity to the ribbon so that its ends will be spaced from the ribbon only about one half mil. The curvature thereof is preferably such that, at the center of the curved surface (that is, behind the point of attachment of the needle to the ribbon), the stationary electrode will be spaced about 2 or 3 mils from the ribbon. Since the most active portion of the ribbon is in the region around the point of attachment of the needle thereto, it is apparent that this region may be moved by the needle a distance just slightly less than 2 or 3 mils without touching the stationary electrode.

Bel However, since the spacing between the two electrodes is much smaller than in the case of the pick-up constructions disclosed by Sinnett in his aforementioned copending application, it is apparent that, for a given excursion of the needle, or a given movement of the ribbon electrode, the percentage change in capacity will be much greater. Consequently, it follows that the pickup device will be much more sensitive.

The novel features that I'consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of one embodiment thereof when read in connection with the accompanying drawing, in which Figure 1 is a perspective view of a pick-up device constructed according to my present invention and with the cover thereof removed,

Figure 2 is a sectional View taken substantially along the line II-II of Figure 1,

Figure 3 is a sectional view taken along the line III-III of Figure 1,

Figures 4 and 5 are diagrammatic views illustrating the manner of operation and advantages of my present invention.

Referring more particularly to the drawing, wherein similar reference characters designate corresponding parts throughout, there is shown a supporting yoke I which may be of brass or any other suitable, electrically conductive material and which has a pair of forwardly extending arms 3, the yoke I being also formed with a transverse slot 5 to provide a hinge section Ia and a relatively ixed section I b, The bottom of the yoke portion Ib is cut away along converging planes in a direction from the yoke portion Ia toward the arms 3, as best shown in Figure 3, to thereby provide the lower ends of the arms 3 with thin, curved shoulders 3a. IA strip or ribbon I of ilexible, resilient, conductive material extends around the shoulders 3a to span the space between the yoke arms 3 and has its ends clamped against the yoke part Ia by means of clamping blocks 9 and screws II. A screw I3 threadedly received in the hinge part Ia and bearing against the rear face of the portion Ib of the supporting block is adjustable to impart more or less tension to the vibratory portion 'Ia of the ribbon 'I which extends across the space between the arms 3. The ribbon 1 may be made of nickelsteel alloy or of any other suitable material having a thickness of about 2 or 3 mils and a width of about le to about 52 inch. These dimensions are not critical, however, and may be varied to suit particular requirements. Since the distance between the yoke-arm shoulders 3a is iixed, the length of the vibratory ribbon portion la will always be the same no matter how much tension is applied to the ribbon, and therefore the resonant frequency of the ribbon portion 'Ia will always remain constant.

Slidably mounted on the supporting block I between the arms 3 for lineal movement toward and away from the vibratory ribbon portion 'Ia is a block I5 of insulating material. The block I5 may be supported on the arms 3 by a pair of screws I'I which are threadedly received therein and which extend through slots I9 in the arms 3. By merely loosening the screws I'I, the block I5 may be adjusted in one direction or the other to the desired position, after which the screws I'I may be tightened to hold the block I5 in place.

4Opposite the vibratory ribbon portion "la, there is mounted on the insulating block l5 a conductive plate 2l having a concave or other suitably curved, front surface Zia which faces the normally plane, opposing surface of the ribbon portion Ia. Preferably, the block l5 is adjusted on the arms 3 to such a position that the end porti-ons thereof will be spaced from the vibratory ribbon portion la only about 1/2 mil. The curvature of the front surface 2id of the conductive member or electrode 2i may be part of any suitable surface of revolution but is preferably part of an ellipse of such shape that, at its center, it is spaced from the ribbon portion la only about 11/2 to 21/2 mils. In the drawing, however, the curvature has been greatly exaggerated for the sake of clearne'ss.

The conductive plate 2l acts as the stationary electrode and cooperates with the vibratory portion la of the ribbon from which it is separated by an air space or by other suitable dielectric material to constitute a capacitor. Secured to the upper portion of the front face of the block I5 is an anchoring block 2t to which the upper end of a needle 25 of piano Wire or the like may be secured, as by solder 2l. The vertical shank of the needle 25 is also Isoldered to the ribbon portion 'la'by a solder connection 29. Below the ribbon portion la the needle 25 has a right angled bend and terminates in a loop or holder 3| which carries a tip 33 of sapphire or the like adapted to engage in and cooperate with the groove of a phonograph record.

During operation, the record groove rides under the needle tip 33 and causes the needle to vibrate. In turn, the needle 25 imparts vibratory movement to the ribbon portion la. relative to the fixed or stationary plate 2l to thereby vary the capacitance of the capacitor la, 2l. Connection is preferably made from this capacitor to a suit-I able transmission line (not shown) one conductor of which is preferably grounded and Connected to the supporting yoke l with which the ribbon l has electrical connection, and the other or high potential conductor of which is connected by a lead 35 to the stationary electrode 2l. The output of the pick-up device may then be connected across a tuning inductor in the input circuit of a suitable vacuum tube oscillator which has been tuned to a desired mid-frequency to thereby provide frequency modulated signals in a manner more fully set forth and claimed in a copending application of Chester M. Sinnett, Serial No. 459,375, filed September 23, 1942, and also assigned to the Radio Corporation of Amer-ica.

A. pick-up device as above described will have much greater sensitivity than similar pick-up devices heretofore known. The reason for this can be better understood by reference to Figures 4 and 5. In these gures, the stationary plate 2| and the ribbon portion 'la are shown diagrammatically. In Figure 4, the stationary plate 2| is shown having a plane surface facing the ribbon portion la. The ribbon portion la, in approaching the stationary electrode 2l in response to signal forces applied thereto by the needle, moves from the solid line position to the dotted line position. The greatest change of capacity per unit area of each electrode will, obviously, take place in the central regions of the electrodes 'la and 2l. To prevent the central region of the vibratory ribbon portion 'la from contacting the opposed, plane surface of the stationary electrode 2l, the separation between these electrodes must be greater than the distance which the ribbon portion 'la is displaced at its center. In the regions adjacent the ends of the electrodes 7a and 2| there is practically no relative movement and, therefore, the change in capacity per unit area of electrodes is practically nil. By forming the front surface 2i a of the stationary electrode along a suitably concaved curve, its ends 2lb can be brought very close to the adjacent parts of the ribbon portion la, as clearly shown in Figure `5. AIn this case, when the ribbon portion 1a moves from the solid line position to the dotted line position so that its normally plane surface Which faces the curved surface Zia assumes a lsubstantially convex shape tending to approach a shape complemental to the curved surface 2| a, it Will be apparent that there will be a change in capacity along practically the entire overlapping area of ythe two electrodes. This, coupled lWith the fact that the initial capacity is smallerthan when the electrodes are shaped and arranged as in Figure ll, produces a much larger relative change in capacity and hence provides much greater sensitivity.

From the foregoing description, it will be apparent to tho-se skilled in the art that I have provided an improved capacity type pick-up which will provide improved results over similar pick-ups of the prior art. Although I have shown and described only a single embodiment of my invention, it will undoubtedly be apparent to those skilled in the art that many other forms thereof, as well as changes in the particular one described, are possible. For example, instead of making the surface 2da curved on a surface of revolution, it may be made ISubstantially V-shaped or of any other non-planar form. It will also be apparent, no doubt, that my present invention is applicable to microphones, loudspeakers, and to other signal translating devices and not merely to pick-up devices suitable for use with phonographs. Since this invention is capable of various uses and may be made in many forms, I desire that my invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

l. In a signal translating device, a pair of relatively movable, conductive members having an air gap therebetween whereby they are spaced from each other to constitute a capacitor, one of said members having a normally curved surface facing the proximate surface of the other of said members, and said members being so constructed and arranged that, during relative motion therebetween, said surfaces will at times have shapes Which have a non-complemental relation and at other times will have shapes which tend to approach a complemental relation.

2. In a signal translating device, a stationary, conductive member, and a second conductive member vibratively mounted in cooperative relation to said stationary member, said members having a dielectric therebetween and constituting a capacitor, said stationary member having a concave surface which is a portion of an ellipse facing said vibrative member, and said vibrative member being movable relative to said stationary member in response to signal forces applied thereto to thereby vary the capacitance of said capacitor.

3. In a signal translating device, a stationary, conductive member, and a second conductive member of flexible material vibratively mounted in cooperative relation to said stationary member, said members having a dielectric therebetween and constituting a capacitor, said stationary member having a curved surface facing said vibrative member and said vibrative member having a surface facing said curved surface which is normally of a different contour than said curved surface, and said vibrative member being movable relative to said stationary member whereby its said facing surface is deformable into a shape approaching a complemental relation with that of said curved surface to thereby vary the capacitance of said capacitor.

4. A signal translating device according to claim 1 wherein said curved surface is concave, and wherein said shape approaching complemental relation with that of said concave surface is substantially conveX.

5. In a signal translating device, a stationary, conductive member, and a flexible, conductive member having a portion vibratively mounted in cooperative relation to said stationary member and movable relative to said stationary member in response to signal forces applied thereto, said members having a dielectric therebetween and constituting a capacitor, said stationary member having a concave surface facing said vibrative portion, and said vibrative portion having a normally plane surface facing said concave surface, said plane surface being deformable upon movement of said vibrative portion toward said stationary member into a substantially convex shape approaching a complement-al relation with that of said concave surface.

6. A signal translating device according to claim 5 characterized in that said flexible member is made of a strip of resilient material, and characterized further by the addition of means for placing said vibrative strip portion under more or less tension.

7. A signal translating device according to claim 5 characterized by the addition of a needle carried by said vibrative portion for cooperation with the groove of a phonograph record.

8. A phonograph record signal translating device comprising a support, a yieldable conductive member vibratively carried by said support, a member of insulating material movably mounted on said support for adjustment thereon relative to said vibrative member, a second conductive member carried by said insulating member in cooperative, spaced relation to said vibrative member, said conductive members having a dielectric therebetween and constituting a capacitor, said insulating member being adjustable on said support to vary the spacing between said conductive members, said second conductive member having a concave surface facing said vibrative member, and said vibrative member having a normally plane surface facing said concave surface, and a needle carried by said vibrative member for cooperation with a record, the movement of said needle in response to the record imparting Vibratory motion to said vibrative member relative to said second conductive member to thereby vary the capacitance of said capacitor, and said needle being connected to a point on said vibrative member such that when said needle causes said vibrative member to move toward said concave surface its normally plane surface will be deformed into a convex surface tending to approach a complemental relation with that of said concave surface.

9. A phonograph record signal translating device according to claim 8 wherein said support comprises a yoke terminating in a pair of spaced arms, characterized further in that said yieldable conductive member comprises a strip of resilient material mounted across the ends of said arms whereby to span the space therebetween, and characterized further in that said member of insulating material comprises a block adjustably mounted between said arms for movement toward and away from,said strip.

RENE SNEPVANGERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,957,512 Weinberger May 2, 1934 1,786,436 Leilier Dec. 30, 1930 2,322,621 Farrow June 22, 1943 1,777,397 Crozier Oct. 7, 1930 FOREIGN PATENTS Number Country Date 332,996 British Aug. 7, 1930 524,619 British Aug. 12, 1940 310,762 British Apr. 30, 1929 

